In general, an analog multiplexer has a plurality of inputs, respectively coupled to one output via corresponding internal channels.
Each corresponding internal channel conventionally has a driveable circuit produced in an integrated fashion, such as a switching circuit under the control of at least one corresponding drive signal.
When an internal channel is selected by means of the at least one corresponding drive signal, the analog multiplexer allows transmission of data from the corresponding input of the first group and the terminal of the second group.
When the multiplexer is operating in the so-called “cold spare” mode, the power supply of this multiplexer is cut off completely, but the multiplexer can receive one or more external signals at its inputs or at its output, these being delivered for example by another multiplexer in normal operation.
In general, the multiplexer compatible with the so-called “cold spare” mode is configured so as not to be damaged by the signal or signals present at its inputs and/or at its output, while minimizing current consumptions at its inputs and at its output.
U.S. Pat. No. 9,520,869, incorporated by reference, is known from the prior art, and describes an analog multiplexer where the high-voltage analog switching circuits are compatible with a low-voltage drive technology and the so-called “cold spare” mode. The analog switching circuits are furthermore configured in order to ensure linearity and operation of the switching circuits and to reduce as much as possible the leakage currents of the switching circuits when the latter are in their off state.
In certain situations of voltages present at the input and at the output, however, the corresponding switching circuits may be off, which makes the multiplexer not entirely bidirectional.
Furthermore, this multiplexer of the prior art does not have any circuit for protection against a possible excessively high current flowing in one of the switching circuits, running the risk of destroying the corresponding switching circuit.
There is thus a need to provide an analog multiplexer which is fully bidirectional while furthermore preferably having protection against a short circuit at the input or at the output of any one of its switching circuits, which might give rise to a high current flowing in the corresponding switching circuit.